1. Field of the Invention
This invention relates to a method of manufacturing an electron-emitting device, an electron source and an image-forming apparatus comprising such an electron source and, more particularly, it relates to a method of manufacturing the same by means of an ink-jet technique.
2. Related Background Art
Two types of electron-emitting devices have been known; the thermoelectron emission type and the cold cathode electron emission type. Of these, the cold cathode emission type refers to devices including field emission type (hereinafter referred to as the FE type) devices, metal/insulation layer/metal type (hereinafter referred to as the MIM type) electron-emitting devices and surface conduction electron-emitting devices. Examples of FE type device include those proposed by W. P. Dyke & W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "PHYSICAL Properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 5248 (1976). Examples of MIM device are disclosed in papers including C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32, 646 (1961).
Examples of surface conduction electron-emitting devices include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10, 1290, (1965).
A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface. While Elinson et al. proposes the use of SnO.sub.2 thin film for a device of this type, the use of Au thin film is proposed in [G. Dittmer: "Thin Solid Films", 9, 317 (1972)] whereas the use of In.sub.2 O.sub.3 /SnO.sub.2 thin film and that of carbon thin film are discussed respectively in [M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)] and [H. Araki et al.: "Vacuum", Vol. 26, No. 1, p. 22 (1983)].
FIG. 18 of the accompanying drawings schematically illustrates a typical surface conduction electron-emitting device proposed by M. Hartwell. In FIG. 18, reference numeral 1 denotes a substrate. Reference numeral 4 denotes an electroconductive thin film normally prepared by producing an H-shaped thin metal oxide film by means of sputtering, part of which is subsequently turned into an electron-emitting region 5 when it is subjected to a process of current conduction treatment referred to as "energization forming" as described hereinafter. In FIG. 18, a pair of device electrodes are separated from each other by a distance L of 0.5 to 1 mm and the central area of the electroconductive thin film has a width W' of 0.1 mm.
Apart from the above device, the applicant of the present patent application has proposed a surface conduction electron-emitting device prepared by arranging a pair of device electrodes and an electroconductive thin film on a substrate in different manufacturing steps as typically described in Japanese Patent Application Laid-Open No. 7-235255. FIGS. 19A and 19B schematically illustrate the proposed surface conduction electron-emitting device. The electroconductive thin film arranged between a pair of device electrodes 2 and 3 is preferably made from electroconductive fine particles in order to produce an electron-emitting region that operates in a desired manner. For instance, a film made from fine particles of palladium oxide PdO is preferably used for the electroconductive thin film.
Conventionally, an electron emitting region 5 is produced in a surface conduction electron-emitting device by subjecting the electroconductive thin film 4 of the device to a current conduction treatment which is referred to as "energization forming". In an energization forming process, a constant DC voltage or a slowly rising DC voltage that rises typically at a rate of 1V/min. is applied to given opposite ends of the electroconductive thin film 4 to partly destroy, deform or transform the film and produce an electron-emitting region 5 which is electrically highly resistive. Thus, the electron-emitting region 5 is part of the electroconductive thin film 4 that typically contains a fissure or fissures therein so that electrons may be emitted from the fissure and its vicinity. Note that, once subjected to an energization forming process, a surface conduction electron-emitting device comes to emit electrons from its electron emitting region 5 whenever an appropriate voltage is applied to the electroconductive thin film 4 to make an electric current run through the device.
With the above described energization forming process of producing an electron-emitting region, however, it is difficult to satisfactorily control the process, particularly in terms of where in the electroconductive thin film the electron-emitting region is produced and what profile it has so that, when a large number of electron-emitting devices are subjected to an energization forming process, the produced electron-emitting regions may vary from device to device in terms of the location in the electroconductive thin film and the profile. In some cases, the electron-emitting region can show a profile meandering between the device electrodes. Such variances in the location and profile are reflected in the electron-emitting performance of the devices so that the emission current Ie and the electron emission efficiency (the ratio of the emission current to the current flowing through the device If or .eta.=Ie/If) can vary from device to device.
Thus, when a large number of electron-emitting devices are arranged on a substrate to form an image-forming apparatus, and a video signal is applied thereto to produce a uniform brightness, the emission current of the electron-emitting devices can vary from device to device to give rise to an image having irregular brightness, to the detriment of the performance of the apparatus.
Particularly, if the electron-emitting region of an electron-emitting device meanders to a large extent, the diameter of the electron beam emitted from it can expand to produce a large bright spot on the fluorescent film of the image-forming apparatus. Thus, when pixels are densely arranged at a high pitch in order to display finely defined images, the electron beam emitted from an electron-emitting device having a meandering electron-emitting region can partly irradiate one or more than one neighboring pixels to seriously degrade the quality of the displayed image.
The applicant of the present patent application has so far proposed several techniques that can bypass the above identified problem. For instance, Japanese Patent Application Laid-Open No. 1-112633 discloses a method of controlling the location of the electron-emitting region in an electron-emitting device by forming an electroconductive thin film of two electroconductive members having different melting points and forming subsequently an electron-emitting region at a position located along the border line of the two different electroconductive members. Japanese Patent Application Laid-Open No. 2-247940 discloses a technique of arranging a step-forming member at a position for producing an electron-emitting region and forming an electroconductive thin film across the step-forming member to produce a step there, along which an electron-emitting region is formed thereafter. Japanese Patent Application Laid-Open No. 8-96699 teaches a technique of using a pair of device electrodes having different film thicknesses and forming an electron-emitting region along an edge of the device electrode having the greater thickness. Finally, Japanese Patent Application Laid-Open No. 7-325279 teaches a technique of modifying the composition of part of the electroconductive thin film by irradiating it locally with a laser beam to increase the electric resistance there and turning it into an electron-emitting region by energization forming.
As described above, a number of methods have been proposed for controlling the electron-emitting region in terms of position and profile in the process of producing it by energization forming. All these methods are designed to modify part of the electroconductive thin film of an electron-emitting device in order to differentiate it compositionally from the remaining portion of the electroconductive thin film by means of a specifically designed technique such as the use of laser beam or a fine processing operation involving the use of a specifically designed member for producing a projection on the device or the use of a sharp edge formed on one of the device electrodes.